1. Field of the Invention
The present invention relates to a radar that detects a target by transmitting and receiving radio waves generated by performing frequency modulation of continuous waves.
2. Description of the Related Art
An FM-CW radar that detects a target by transmitting and receiving radio waves generated by performing frequency modulation (FM) of continuous waves (CW) transmits a transmitting signal such that an up-modulating interval in which the frequency gradually increases and a down-modulating interval in which the frequency gradually decreases change repeatedly with respect to time in the form of a triangular wave, and receives a reception signal including reflected signals from the target, whereby a relative distance to the target and its relative speed are determined based on the frequency spectrum of a beat signal representing a frequency difference between the transmitting signal and the reception signal. Also, by performing the above-described operation for one beam directed to a predetermined bearing, and by sequentially changing the beam bearing, detection of targets in a predetermined bearing-angle range is performed.
When there is a single target, at the up-modulating interval and the down-modulating interval, a peak appears in the frequency spectrum of a beat signal based on reflected waves from the target. Thus, based on the frequency (hereinafter referred to as the “upbeat frequency”) of the beat signal at the up-modulating interval and the frequency (hereinafter referred to as the “downbeat frequency”) of the beat signal in the down-modulating interval, a relative distance to the target and its relative speed are determined.
However, when there is a plurality of targets in a scanning range, for a single beam, many peaks appear in the frequency spectrum at both the up-modulating interval and the down-modulating interval. For this reason, there is a risk in that an error may occur in combining (hereinafter referred to as “pairing”) a plurality of upbeat frequencies and a plurality of downbeat frequencies.
In radar (1), described in Japanese Patent No. 2765767 (Japanese Patent Application No. 03-114621), a radar is disclosed in which peaks in frequency spectrums having substantially identical signal intensities are selected as the peaks resulting from the same target. Furthermore, in radar (2) described in Japanese Unexamined Patent Application Publication No. 2000-65921, a radar is disclosed in which peaks which appear in the frequency spectrums at an up-modulating interval and peaks which appear in the frequency spectrum at a down-modulating interval are paired by those peaks having identical representative beam bearings.
However, in the above-described radar (1), when there is a plurality of peaks of substantially identical signal intensities in the frequency spectrums, pairing is not adequately performed. Furthermore, in the above-described radar (2), when there is a plurality of peak groups having identical representative beam bearings, pairing is not adequately performed.